This proposal constitutes a broad clinical research program which replaces the previously funded grant entitled, "Regulation of Thyroid Hormone Deiodination in Man." For organizational purposes, the program is divided into the following general categories: (1) hypothalamic- pituitary studies, (2) thyroid function, and (3) peripheral thyroid hormone metabolism. In each of these categories there are a number of studies which are designed to develop new insights into normal and abnormal human thyroid function. In almost all of these proposed studies, measurements of thyroidal iodine release and thyroid hormone deiodination are utilized which are methods developed in this laboratory. The renaming of this research program was felt to be more appropriate and consistent with the broader application of these research methods.